Lubricating oil refining process

ABSTRACT

A PROCESS FOR THE REFINING OF LUBRICATING OILS BY SOLVENT EXTRACTION OF A LUBRICATING OIL FRACTION FROM PARAFFIN BASE CRUDE TO FORM AN INTERMEDIATE VISCOSITY INDEX LUBRICATING OIL STOCK, DEWAXING THE INTERMEDIATE VISCOSITY INDEX LUBRICATING OIL STOCK AND SOLVENT FRACTIONATING THE DEWAXED STOCK TO PRODUCE A HIGH VISCOSITY INDEX LUBRICATING OIL STOCK AND A LOW VISCOSITY INDEX LUBRICATING OIL STOCK. THE INTERMEDIATE VISCOSITY INDEX LUBRICATING OIL STOCK MAY BE FINISHED PRIOR TO SOLVENT FRACTIONATION BY ACID TREATING, CLAY CONTACTING OR HYDROTREATING. THE SOLVENT EMPLOYED IN THE SOLVENT REFINING STEP MAY BE FURFURAL AND THE SOLVENT EMPLOYED IN THE SOLVENT FRACTIONATION STEP MAY BE NMETHYL-2-PYRROLIDONE.

July 17, 1973 R. A. WOODLE LUBRICATING OIL REFINING PROCESS IVI UnitedStates Patent U.S. Cl. 20S- 36 2 Claims ABSTRACT F THE DISCLOSURE Aprocess for the refining of lubricating oils by solvent extraction of alubricating oil fraction from paraffin base crude to form anintermediate viscosity index lubricating oil stock, dewaxing theintermediate viscosity index lubricating oil stock and solventfractionating the dewaxed stock to produce a high viscosity indexlubricating oil stock and a low viscosity index lubricating oil stock.The intermediate viscosity index lubricating oil stock may be finishedprior to solvent fractionation by acid treating, clay contacting orhydrotreating. The solvent employed in the solvent refining step may befurfural and the solvent employed in the solvent fractionation step maybe N- methyl-Z-pyrrolidone.

BACKGROUND OF THE INVENTION In the manufacture of lubricating oils fromcrude petroleum a number of processing steps are required to incorporatethe desired characteristics in the finished lubricating oil products.These characteristics inlude a selected viscosity range, and dependingupon the quality level, high viscosity index, low pour point, lightcolor, stability, and resistance to oxidation. Stocks for lubricatingoil manufacture are separated from crude petroleum by vacuumdistillation. Typically, several fractions of different boiling rangeare produced thereby providing fractions of different viscosity ranges.The vacuum distillate is then treated by solvent extraction to produce alubricating oil stock of improved viscosity index, i.e., to produce anoil which exhibits relatively little change in Viscosity with change intemperature. The vacuum distillates and solvent refined distillates havea relatively high pour point due to the presence of wax. Typically, waxis removed to produce low pour point lubricating oil stocks by thesolvent dewaxing process. Improved color, stability, and resistance tooxidation are imparted by finishing treatments which may include suchWell known process steps as acid treating, clay contacting, or mildhydrogenation or a combination of such finishing treatments. The solventrefining process also improves the stability of the lubricating oilstock by virtue of the separation of polar compounds and polynaphthenictype materials.

In the solvent extraction process, the oil to be treated is contactedwith a selective solvent which exhibits the desired selectivity for atleast one component of the hydrocarbon charge and the solvent is atleast partially irnmiscible under the conditions of contact in thecontacting zone with the hydrocarbon mixture. Solvents which may beemployed, for example, include furfural, N-methyl-Z- pyrrolidone,nitrobenzene, liquid propane, liquid sulfur dioxide,beta-beta-dichloroether, phenols, and other various well known organicand inorganic selective solvents.

In the solvent dewaxing process, the wax bearing oil is mixed with asolvent having substantially complete solvent action upon the oilcomponent of the wax bearing oil charge and substantially no solventaction upon the wax contained therein at dewaxing temperatures of aboutl0 to -30 F. Such a solvent comprises, for example, a mixture ofaliphatic ketones such as acetone, methyl ethyl ketone, methyl isobutylketone and an aromatic hydrocarbon such as benzene, toluene, or amixture of benzene and toluene. A number of other solvents are knownwhich are useful for effecting separation between a hydrocarbon oil andwax including hydrocarbons less viscous than the oil, for example,naphtha, gasoline, pentanes, butanes, propanes, or mixtures thereof andcertain hydrocarbon derivatives such as dichloromethane, methylenechloride, chloroform, and ethers.

In the use of mild hydrogenation as a lubricating oil finishing step, itis preferred to employ a catalyst such as nickel sulfide-tungstensulfide, molybdenum sulfide, and cobalt molybdate. The hydrogenationstep is conducted at temperatures within the range of about 400 to 750F. and preferably within the range of about 500 to k650 F. Pressures ofabout 100 to 100G p.s.i.g. are employed, preferably of about 200 to 600p.s.i.g. Liquid hourly space velocities of about 0.1 to 3.0 volumes ofoil per volume of catalyst are employed and preferably about 0.5 to 2.0v./v./hr. A hydrogen consumption of about 50 to 200 cubic feet perbarrel of charge stock is employed. Suitably recycle hydrogen rates varywithin the range of about 100 to 1000 standard cubic feet per barrel ofcharge and rates of about 100 to 500 s.c.f./ bbl. are preferred.

In modern petroleum refining technology, high viscosity index productsare manufactured from high viscosity index base oils from parafiiniccrude oils plus the addition of Viscosity index improvers. Theseviscosity index improvers are organic polymers, and they are inherentlyshear unstable. Desirably in the manufacture of premium high viscosityindex products having high Shear stability, it is preferred to use arelatively high viscosity index base oil with a minimum amount ofviscosity index improver. However, the refiner also has a demand forproducts, of a high viscosity index but not requiring maximum shearstability. Accordingly, the refiner needs a process to provideflexibility in the manufacture of high viscosity index lubricating oilssome of which have high shear stability whereas others do not requirethis characteristic. Accordingly, it is an objective of this inventionto provide a method of manufacturing a plurality of viscosity indexgrades of lubricating oil. It is a further objective of this inventionto manufacture a plurality of grades of lubrieating oil in high yieldsin the simplest and most economical way.

SUMMARY OF THE INVENTION In accordance with the process of thisinvention, a Wax distillate such as is produced by the vacuumdistillation of a paraffin base crude oil is treated by a process insequence comprising solvent rening, dewaxing, and solvent fractionation.The solvent fractionation is a second step of solvent extraction inwhich both the raffinate and extract are finished lubricating oilstocks. When employing acid treating, clay contacting, or mildhydrogenation, steps usually referred to as finishing steps, thefinishing step is applied to the dewaxed primary refined oil productprior to fractionation in the second solvent extraction step. Anintermediate VI grade product may also be produced by withdrawal of aportion of the primary refined oil as such product.

In the primary extraction step, any of the solvents referred to abovemay be employed. However, it is preferred to employ furfural orN-methyl-Z-pyrrolidone. Op-

erating conditions are selected to produce a primary raffinate having adewaxed viscosity index of about to and preferably about 90 to 96. Whenemploying furfural as a solvent, extraction temperatures within therange of about to 225 F. and preferably about 170 to 200 F. areemployed. Solvent dosages within the range of about 150 to 600 percentare employed in order to provide the desired VI level. WhenN-methyl-2-pyrrolidone is employed as solvent, solvent extractiontemperatures within the range of 140 to 210 F. are employed andpreferably within the range of 150 to 200 F. with solvent dosages withinthe range of 100 to 500 percent and preferably 150 to 400 percent.

The primary ra'inate is dewaxed to produce a lubricating oil fractionhaving the desired pour point. If desired, the dewaxed oil may besubjected to a linishing treatment for color and stability improvementas described above. The intermediate viscosity index stock is thensubjected to a secondary solvent extraction or solvent fractionation toseparate two lubricating oil fractions, the secondary ratiinate having aviscosity index of at least 100 and preferably about 105 to 125 and thesecondary extract having a viscosity index of about 70 to 95. In thesecondary extraction process it is preferred to employN-methyl-Z-pyrrolidone as solvent since this solvent is capable ofsplitting the' charge into two -inished lubricating oil fractionswithout degrading the color or stability of the extract fraction. Sincethe oil charged to the reextraction step is already a dewaxed andfinished oil, the separation effected in the re-extraction step may becarried out at high temperature, low dosage and at low selectivityconditions. The ability to use much higher temperatures than are usualwith N-methyl-Z-pyrrolidone comes about because refined oil charged tothe re-extraction step is much less miscible with the solvent than thewax distillates from which they are derived. The higher temperatures inturn allow lower solvent dosages to be used. Generally, the extractiontemperatures in the reextraction step are not less than F. nor more than40 F. below the temperature at which the mixture of 6 volumes ofN-methyl-Z-pyrrolidone and 4 volumes of the charge oil became completelymiscible. A preferred extraction temperature is about to 30 F. below theabove detined miscibility temperature. At these temperatures, thesolvent dosage may be varied to produce the desired final high VI levelover a range of yields. The solvent dosage in general is in the range ofabout 100 to 800 volume percent with dosages in the range of 200 to 500volume percent being preferred.

lDESCRIPTION OF THE DRAWING Oil charge, for example, a vacuum distillatefrom paratiin base crude oil is passed through line 11 to primarysolvent contactor 2. In primary solvent contactor 2, oil is contacted incountercurrent flow with a selective solvent, for example, furfuralintroduced into contactor 2 through line 3. Contactor 2 may be anycountercurrent liquid-liquid contacting apparatus such as a columnpacked with Raschig rings or a rotating disc contactor which effectsmultistage countercurrent contacting. The solvent and constituentsextracted from the oil charge pass downwardly through the tower and arewithdrawn as extract through line 4. Treated oil rising throughcontactor 2 containing some dissolved solvent is withdrawn from the topof the tower as rainate through line 5. Extract in line 4 is passed tosolvent stripper 7 wherein the solvent is stripped from the dissolvedconstituents of the oil charge. Extract free of solvent is withdrawnthrough line 8 and recovered solvent is returned to solvent contactor 2through line 3. Rainate in line 5 contains some sol` vent dissolvedtherein and is passed to solvent stripper 9 for recovery of thedissolved solvent. Recovered solvent is withdrawn through line 10 andcombined with the solvent in line 3 to supply the solvent passed tosolvent con;- tactor 2.

Treated oil free of solvent is withdrawn through line 11 and passed todewaxing step 12. Lubricating oil stocks produced from wax distillateshave relatively high pour points due to the presence of wax.Accordingly, in dewaxing step 12 wax is separated from the remaininglubricating oil stock by a process such as solvent dewaxing. In solventdewaxing the wax bearing oil is admixed with a solvent which hassubstantially complete solvent action upon the oil component of the waxyoil charge and substantially no solvent action upon the wax containedtherein at a dewaxing temperature of about +10 to -30 F. Such a solventcomprises, for example, a mixture of 50 percent methylethyl ketone and50 percent toluene. Wax separated from dewaxing step 12 is withdrawnthrough line 13. Dewaxed oil having a pour point of -20 to +20 F. iswithdrawn through line 14. The viscosity index of the dewaxed oil inline 14 is within the range of about 85 to and preferably within therange of about 90 to 96.

Dewaxed lubricating oil stock in line 14 is then passed to Afinishingstep 17 if processing is required to improve the color, stability, oroxidation resistance of the lubricating oil stock. Finishing step 17 maycomprise clay contacting, acid treating, or mild hydrogenation. Treatedoil from finishing step 17 is discharged through line 18. Since the oilin line 18 is an intermediate viscosity index lubricating oil which hasbeen finished, it is suitable for use in blending some grade oflubricating oil and a portion may be withdrawn for such use through line19.

At least a portion of the oil in line 18 is passed to secondary solventcontractor 20. Solvent contractor 20 may be the same type and operatedin a manner similar to that described in connection with contractor 2.The function of solvent contractor 20 is to fractionate the lubricatingoil stock into a high viscosity lubricating oil fraction and a lowviscosity index lubricating oil fraction. This fractionation is done bya solvent extraction technique. However, since both the extract andrainate fractions are intended for use in lubricating oil products, itis necessary that the solvent selected be a highly eiicient solvent toachieve sharp fractionation and it must also effect fraction withoutdegrading the quality of either the rainate or extract fractions.Accordingly, it is preferred to use N-methyl-Z-pyrrolidone as solvent inthe secondary sol-vent contactor. Solvent is introduced into contactor20 through line 21. Extract is withdrawn through line 22 and passed tosolvent stripper 23. In solvent stripper 23, the solvent is recovered asdistillate through line 24 and returned through line 21 to contactor 20.Low VI lubricating oil having a VI within the range of about 65 to 95and preferably 78 to 92 and a pour point within the range of about -10to +20 F. is removed from the bottom of stripper 23 through line 25 andis discharged as product. Rainate from contactor 20 containing a smallamount of dissolved solvent is discharged through line 27 and passed tosolvent stripper 28. In solvent stripper 28, the small amount ofdissolved solvent is withdrawn through line 29 and solvent free high VIlubricating oil fraction is withdrawn from stripper 28 through line 30.The high VI 1ubricating oil has a viscosity index in excess of 100 andpreferably within the range of about to 125 and a pour point of about-10 to +20.

In the process illustrated in the figure, only a single iinishing stepis needed. Optionally finishing step 17 may follow fractionation insecondary solvent contactor 20. In this case, it is necessary toseparately treat each of the high VI, low VI and intermediate VIproducts in separate finishing steps or to treat each of the fractionsas separate batches in the finishing facilities.

DESCRIPTION `OF THE PREFERRED EMBODIMENTS In an example of the processof this invention, a wax distillate is solvent extracted with furfuralusing a dosage of 230 volume percent and an extraction temperature of F.to produce an SAE 20 grade lubricating oil stock. The furfural refinedoil is then dewaxed using methylethyl ketone-toluene as a solvent at afiltration temperature of 0 F. to produce an oil having a pour point of+5 F. The dewaxed-furfural refined oil is then decolorized by hydrogentreatment at 200 p.s.i.g. and 550 F. in the presence of acobalt-molybdenum catalyst. The resulting intermediate viscosity indexlubricating oil has the following tests:

Gravity, API 30.4 Flash, COC F. 435 viscosity, SUS at 210 F. 54.4 5 VI90 Color, Lovibond (6 inch cell) 45 Pour, F +5 The intermediateviscosity index lubricating oil stock is 10 then fractionated bycountercurrent contact with N-methyl-Z-pyrrolidone using a dosage of 200volume percent solvent and a contacting temperature of 220 F.

The raliinate from the N-methyl-2-pyrrolidone fractionation comprises ahigh VI oil and the extract comprises a low VI lubricating oil stock.Tests and yields of the two fractions are as follows:

High vI Low v1 lubricating lubricating oil stock oil stock Gravity, API32.0 26. 0 Flash, Coo, F 435 435 Viscosity SUS at 210 F 52.0 55.0 V 10a75 Color, Lovibond (6 cell) 45 75 Pour, F +10 +5 25 Yield, vol. percentbasis, intermediate VI The high VI lubricating oil stock is suitable formanufacture of premium lubricating oils having high shear stability. Thelow VI lubricating oil stock is suitable for inclusion in those productsnormally made from unextracted oils Where the change in viscosity withtemperature is not critical to performance.

EXAMPLE II In this example, the intermediate VI oil of Example I isfractionated with N-methyl-Z-pyrrolidone employing a solvent dosage of300 volume percent and a contacting temperature of 220 F. The followinglubricating oil stocks are produced:

High VI Low VI lubricating lubricating oil stock oil stock Gravity, API31.8 30.1 Flash, C00, F. 430 435 VI 115 e7 Pour F +10 +5 Yield, vol.percent basis, intermediate VI oil- 10. 0 90. 0

EXAMPLE III In the example, a light solvent neutral oil having aViscosity equivalent to an SAE 7 grade oil is made by furfural refining,solvent dewaxing, and finishing. The neutral oil is then re-extractedusing N-methyl-Z-pyrrolidone at 200 F. and 315 percent solvent dosage.The in- 55 termediate VI lubricating oil fraction from furfural refiningand the high and low VI lubricating oil fractions produced byfractionation with N-methyl-Z-pyrrolidone have the following tests andyields:

Intermediate VI High VI Low VI lubricating lubricating lubricating oilstock oil stock oil stock Gravity, API 31. 5 33. 8 27. 9 Viscosity, SUS210 F 42. 8 42. 5 43. 0 V 9e 111 87 Yield vol. percent basis,intermediate VI oil 100 38 62 6 EXAMPLE 1v In this exam-ple, a Waxdistillate 40 useful in the manufacture of SAE 40 grade lubricating oilsis extracted with furfural at a solvent dosage of 450 volume percent anda temperature of 210 F. to produce a 60 volume percent yield of alubricating oil fraction having a dewaxed VI of 90. The resulting VIlubricating oil fraction is then fractionated usingN-methyl-Z-pyrrolidone at a solvent dosage of 400 percent and at arefining temperature of 200 F. to produce a yield of 33 percentraffinate having a VI of to 66 percent yield of extract having a VI of85.

EXAMPLE V In this example, the charge stock of Example IV is treatedwith N-methyl-2-pyrrolidone at a solvent dosage of 270 percent and atemperature of 200 F. to produce a yield of 40 percent of a 95 dewaxedVI intermediate grade lubricating oil. The resulting intermediate gradelubricating oil is then fractionated with N-methyl-2-pyrrolidone at asolvent dosage of 400 and a refining temperature of 200 F. to produce a50 percent yield of raffinate having a VI of 100 and 50 percent yield ofextract having a VI of 90.

I claim:

1. A process for the production of lubricating oils of improvedproperties which comprises treating a vacuum distillate derived from aparafiin base crude oil with a selective solvent in a first extractionzone forming a first rafiinate and a rst extract, dewaxing said firstrafiinate forming a first lubricating oil stock having a pour point of-10 to +20 F. and a viscosity index of 85 to 100, hydronishing saidfirst lubrication oil and treating at least a portion of said firsthydrofinished lubricating oil stock with N-methyl-Z-pyrrolidone in asecond extraction zone forming a second raflinate comprising a secondlubricating oil stock having a pour point within the range of about -10to +20 F. and a viscosity index in excess of 100 and a second extractcomprising a third lubricating oil stock having a pour point within therange of -10 to +20o F. and a viscosity index within the range of about`65 to '95, the temperature in the second extraction zone being between10 F. and 40 F. below the temperature at which a mixture of six volumesof N-niethyl-Z-pyrrolidone and four volumes of charge oil becomecompletely miscible.

2. The process of claim 1 in which the second extraction zonetemperature is between 15 F. and 30 F. below the miscibilitytemperature.

References Cited UNITED STATES PATENTS 2,952,610 9/1960 Fear 208-363,520,796 7/1970 Murphy et al. 2108-18 3,488,283 1/ 1970 Button et al.208-36 3,472,757 10/ 1969 Morris et al. 208-36 2,967,147 1/ 1961 Cole208-144 HERBERT LEVINE, Primary Examiner U.S. Cl. X.R. 208-18

